Data not update when login is successfull in index.php?

I make a login page like user login. if registered then login with email and password(navigate register.php to index.php page) or sign up if not registered. works good but i want to add update functionality in my index.php page concept is simple if user wants to update its record then he make updations in a form and submit. I make a update query here but its shows Notice: Undefined index: id in C:\wamp\www\LOginKodingMadSimple\index.php on line 34. Where i am wrong ?